Dialkylimidazolium Ionic Liquids Hydrolyze Cellulose Under Mild Conditions

Abstract

The average molecular weight of cellulose derived from filter paper, poplar, and Avicel decreases by up to two orders of magnitude during typical mild dissolution protocols using ionic liquids (ILs). About an order of magnitude greater cellulose depolymerization rate during ionic liquid dissolution occurs in 1-butyl-3-methylimidazolium chloride (BmimCl) and 1-ethyl-3-methylimidazolium chloride (EmimCl) compared to 1-ethyl-3-methylimidazolium acetate (EmimOAc), and, unintuitively, greater IL purity results in greater cellulose depolymerization. The following data support the mechanism of cellulose hydrolysis to be acid-catalyzed: (i) increase in number of reducing ends following cellulose dissolution in IL; (ii) addition of N-methylimidazolium base suppresses cellulose depolymerization during dissolution in IL; (iii) small amounts of glucose and traces of hydroxymethyl furfural are present following cellulose dissolution in IL. The acid is presumably synthesized via IL decomposition to generate a carbene and proton, consistent with hypothesis derived from molecular modeling. Titration experiments conducted here measure the amount of acid synthesized to be in the 4000 ppm range for high-purity BmimCl IL during mild processing conditions for cellulose dissolution. This data is relevant for understanding the extent of IL decomposition during biomass dissolution.

Thermal and Viscoelastic Properties of Cellulosic Gels with Different Ionic Liquids and Coagulation Agents

“…The difference in transparency might suggest a difference in structure between BMIMCl and EMIMAc gels, which may be expected since the molecular weight of cellulose in BMIMCl solutions was different (lower) than in EMIMAc solutions (Gazit and Katz 2012).…”

Reversible Carbene Formation in the Ionic Liquid 1‐Ethyl‐3‐Methylimidazolium Acetate by Vaporization and Condensation

“…For example, for sodium acetate this vibration was reported at 1578 (s) cm À1 , [17] and in [1][AcO À ]i ti sf ound at 1575 cm À1 (Figure 2g). This indicates that after condensation at 9K,b oth AcOH and AcO À are presenti nt he solid film.…”

“…[7] However, the strong 725 and 705 cm À1 bandsa re not observed in these experiments, and a1 205 cm À1 band that might correspond to our 1208 cm À1 absorption was assignedi n1CCCTfO À to aS O 3 deformation mode of TfO À . The absence of absorption bands that could be attributed to the acetate anion AcO À or to the imidazolium cation 1 [7] indicatest hat the evaporation of [1][AcO À ]r esultsi np roton transfer and in the formation of neutral EMIm 2 and AcOH, and that ion pairs are not stable in the gas phase. There is also no evidencef or hydrogen-bonded aggregates between 2 and AcOH.…”

“…In the second set of experiments, [1][AcO À ]w as slowly evaporated and the vapor directly condensed on aC sI window at 9K (Figure 2b,T able 2) without inert gas to form as olid film. The IR spectrum obtained under these conditions shows two strong absorptions in the C=Os tretching region:aband with am aximum at 1716cm…”

Catalytic Depolymerization of Microcrystalline Cellulose Accomplished in an Ionic Liquid

“…Catalysts utilized have included sulfuric, hydrochloric, and IL-based acid catalysts (Amarasekara and Wiredu, 2011;Gazit and Katz, 2012;Gazit and Katz, 2012;Li et al, 2007;Li et al, 2008;McIlvaine et al, 2010;Meine et al, 2012;Rinaldi and Schüth, 2009;Su et al, 2011;Watanabe, 2010;Zhang et al, 2010). Breakdown products include the monomer, cellobiose, (which is two glucose units), glucose, 5-hydroxymethylfurfural (HMF) and other components (McIlvaine et al, 2010).…”